1. Field of the Invention
The invention generally relates to photographic cameras adapted to receive a filmstrip having a leader, wherein a rotary take-up spool includes a plurality of engaging members for engaging the leader to wind the filmstrip onto the spool. More particularly, the invention relates to apparatus for properly positioning the leader with respect to the spool in the event the leader is improperly positioned, initially. 2. Description of the Prior Art
As is well known, 35mm film conventionally includes a row of perforations adjacent each of its longitudinal edges. The perforations are utilized, among other purposes, for film advance in a camera. Typically, the advance mechanism in the camera includes a sprocket wheel having a plurality of teeth which engage the filmstrip in its perforations to pull the filmstrip in increments across an exposure window. A film take-up spool is coupled to the sprocket wheel, often by a slipping clutch assembly to compensate for the varying thickness of the film roll on the spool as more of the exposed film is wound onto the spool. The filmstrip is provided in a light-tight cartridge which may be loaded in the camera in daylight. A leader portion of the filmstrip extends from the cartridge through a light-trapping opening and usually has a tongue-shaped configuration of a width which is approximately half the width of the remainder of the filmstrip. When the cartridge is loaded in the camera, the film leader is intially located with its single row of edge perforations in the operating region of several teeth circumferentially disposed in coplanar relation on the take-up spool. As the spool is rotated, one or more of the teeth engage the leader in its perforations to wind the leader onto the spool. A spring-like deflector may be provided, for example, on the back door of the camera for pressing the leader against the spool to ensure engagement of the leader by the teeth on the spool.
When the cartridge is loaded in the camera, the tongue-shaped leader may be inclined with respect to the axes of rotation of the take-up spool to such an extent that the row of perforations in the leader is situated outside the operating region of the teeth on the spool. Consequently, the leader cannot be secured to the spool. This problem is addressed in U.S. Pat. No. 4,451,011. According to the patent, the teeth on the take-up spool are offset from one another in an axial direction, as well as in a circumferential direction, to engage the leader in its perforations even in the event of inclined introduction of the leader into the camera. Such a proposed solution is not without its shortcomings, however. Although one or more of the teeth will engage the leader in an inclined position with respect to the axis of the spool, it appears that the leader may not be properly wound onto the spool because the leader will remain in the inclined position. As a result, the filmstrip will be wound on the spool in a helix and a film jam may result.
Another approach is disclosed in U.S. Pat. No. 3,484,053. In that patent, it is proposed that a tongue-shaped leader initially in an inclined position with respect to the axis of the take-up spool be displaced to a non-inclined position with respect to the axis before the leader can be engaged by the teeth on the spool. According to the patent, the take-up spool has a pair of coaxial portions of slightly different diameters. The teeth are circumferentially disposed in co-planar relation on the spool portion of smaller diameter. The spool portion of larger diameter terminates at its junction with the spool portion of smaller diameter in a sharp edge which extends around the axis of the take-up spool along a helix having a single convolution. During rotation of the take-up spool, the helical edge of the spool portion of larger diameter abuts a longitudinal edge of the leader as the leader is wound onto the spool portion of smaller diameter. Whenever the leader is in an inclined position, the helical edge displaces the leader until it is located in a non-inclined position, in the operating region of the teeth. Thus, the teeth can engage the leader in its perforations and the leader can be properly wound onto the spool portion of smaller diameter. The wider remainder of the filmstrip is wound onto the pair of spool portions after approximately two convolutions of the leader are wound on the spool portion of smaller diameter.
Although the approach disclosed in U.S. Pat. No. 3,484,053 might appear preferable to the one disclosed in U.S. Pat. No. 4,451,011, it too is not without its shortcomings. For example, a leader in an inclined position may overlap the helical edge of the spool portion of larger diameter, in which case the helical edge may not abut the longitudinal edge of the leader to displace the leader to the non-inclined position.